User terminal, radio base station, radio communication method and radio communication system

ABSTRACT

The present invention is designed to prevent producing interference with UL signals even when a user terminal caries out LBT in a system in which LTE/LTE-A is run in an unlicensed band. A user terminal according to one aspect of the present invention provides a user terminal that can communicate by using an unlicensed band, and this user terminal has a receiving process section that detects a channel state in the unlicensed band by performing LBT (Listen Before Talk) in a sensing subframe, and a control section that controls a predetermined subframe as the sensing subframe based on a sensing pattern.

TECHNICAL FIELD

The present invention relates to a user terminal, a radio base station,a radio communication method and a radio communication system that areapplicable to next-generation communication systems.

BACKGROUND ART

In the UMTS (Universal Mobile Telecommunications System) network, thespecifications of long term evolution (LTE) have been drafted for thepurpose of further increasing high speed data rates, providing lowerdelays and so on (see non-patent literature 1). In LTE, asmultiple-access schemes, a scheme that is based on OFDMA (OrthogonalFrequency Division Multiple Access) is used in downlink channels(downlink), and a scheme that is based on SC-FDMA (Single CarrierFrequency Division Multiple Access) is used in uplink channels (uplink).Also, successor systems of LTE (also referred to as, for example,“LTE-advanced” or “LTE enhancement” (hereinafter referred to as“LTE-A”)) have been developed for the purpose of achieving furtherbroadbandization and increased speed beyond LTE, and the specificationsthereof have been drafted (Rel. 10/11).

In relationship to LTE-A systems, a HetNet (Heterogeneous Network), inwhich small cells (for example, pico cells, femto cells and so on), eachhaving local a coverage area of a radius of approximately several tensof meters, are formed within a macro cell having a wide coverage area ofa radius of approximately several kilometers, is under study. Also, inrelationship to HetNets, a study is in progress to use carriers ofdifferent frequency bands between macro cells (macro base stations) andsmall cells (small base stations), in addition to carriers of the samefrequency band.

Furthermore, in relationship to future radio communication systems (Rel.12 and later versions), a system (“LTE-U” (LTE Unlicensed)) to run anLTE system not only in frequency bands that are licensed tocommunications providers (operators) (licensed bands), but also infrequency bands that do not require license (unlicensed bands), is understudy. In LTE-U operations, a mode that is premised upon coordinationwith licensed band LTE is referred to as “LAA” (Licensed-AssistedAccess) or “LAA-LTE. Note that systems that run LTE/LTE-A in unlicensedbands may be collectively referred to as “LAA,” “LTE-U,” “U-LTE,” and soon.

While a licensed band refers to a band in which a specific operator isallowed exclusive use, an unlicensed band (also referred to as“non-licensed band”) refers to a band which is not limited to a specificprovider and in which radio stations can be provided. Unlicensed bandsinclude, for example, the 2.4 GHz band and the 5 GHz band where Wi-Fi(registered trademark) and Bluetooth (registered trademark) can be used,the 60 GHz band where millimeter-wave radars can be used, and so on.Studies are in progress to use such unlicensed bands in small cells.

CITATION LIST Non-Patent Literature

Non-Patent Literature 1: 3GPP TS 36.300 “Evolved Universal TerrestrialRadio Access (E-UTRA) and Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN); Overall Description; Stage 2”

SUMMARY OF INVENTION Technical Problem

Existing LTE presumes operations in licensed bands, and therefore eachoperator is allocated a different frequency band. However, unlike alicensed band, an unlicensed band is not limited to use by a specificprovider. Furthermore, unlike a licensed band, an unlicensed band is notlimited to use in a specific radio system (for example, LTE, Wi-Fi,etc.). Consequently, there is a possibility that the frequency bandwhich a given operator uses in LAA overlaps the frequency band whichanother operator uses in LAA and/or Wi-Fi.

When an LTE/LTE-A system (LTE-U) is run in an unlicensed band, differentoperators and/or non-operators may set up radio access points (alsoreferred to as “APs,” “TPs,” etc.) and/or radio base stations (eNBs)without even coordinating and/or cooperating with each other. In thiscase, detailed cell planning is not possible, and, furthermore,interference control is not possible, and therefore significantcross-interference might be produced in the unlicensed band, unlike alicensed band.

In order to prevent cross-interference in unlicensed bands, a study isin progress to allow an LTE-U base station/user terminal to perform“listening” before transmitting signals and check whether other basestations/user terminals are engaged in communication. This listeningoperation is also referred to as “LBT” (Listen Before Talk).

There is a demand to introduce LBT functions for UL (UL-LBT) in userterminals in order to prevent interference with UL signals (uplinksignals) in LAA systems. However, UL-LBT has never been studiedheretofore, and no frame configuration that is suitable for UL-LBT hasbeen proposed so far. In particular, unless the subframes for carryingout LBT sensing and/or the time length of sensing are configuredadequately, it may not be possible to prevent producing interferencewith UL signals.

The present invention has been made in view of the above, and it istherefore an object of the present invention to provide a user terminal,a radio base station, a radio communication method and a radiocommunication system which can prevent producing interference with ULsignals even when user terminals use LBT in systems that run LTE/LTE-Ain unlicensed bands.

Solution to Problem

According to one aspect of the present invention, a user terminal cancommunicate with a radio base station by using an unlicensed band, andthis user terminal has a receiving process section that detects achannel state in the unlicensed band by performing LBT (Listen BeforeTalk) in a sensing subframe, and a control section that controls apredetermined subframe as the sensing subframe based on a sensingpattern.

Advantageous Effects of Invention

According to the present invention, it is possible to prevent producinginterference with UL signals even when user terminals use LBT in systemsthat run LTE/LTE-A in unlicensed bands.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 provide diagrams to show examples of modes of radio communicationsystems that use LTE in unlicensed bands;

FIG. 2 is a diagram to show an example of a mode of a radiocommunication system that uses LTE in an unlicensed band;

FIG. 3 provide diagrams to explain examples of operating agents in LBTin a system in which LTE/LTE-A is run in an unlicensed band;

FIG. 4 is a diagram to show examples of frame configurations for LBT ina system in which LTE/LTE-A is run in an unlicensed band;

FIG. 5 is a flowchart to show an example of UL-LBT processes in a userterminal according to the present invention;

FIG. 6 is a diagram to show examples of associations of TDD UL/DLconfigurations and sensing patterns;

FIG. 7 is a diagram to show examples of special subframe configurationsin TDD;

FIG. 8 is a diagram to show examples of sensing subframe configurationsin TDD;

FIG. 9 is a diagram to show examples of associations of TDD UL/DLconfigurations and sensing patterns;

FIG. 10 provide diagrams to show examples of sensing patterns to beconfigured implicitly;

FIG. 11 is a diagram to show examples of sensing patterns to be reportedexplicitly;

FIG. 12 provide diagrams to show examples where cell-specific sensingpatterns are reported explicitly;

FIG. 13 provide diagrams to show examples where user terminal-specificsensing patterns are reported explicitly;

FIG. 14 is a flowchart to show an example of sensing subframe switchingprocesses in a third embodiment;

FIG. 15 is a diagram to show an example of a schematic structure of aradio communication system according to an embodiment of the presentinvention;

FIG. 16 is a diagram to show an example of an overall structure of aradio base station according to an embodiment of the present invention;

FIG. 17 is a diagram to show an example of a functional structure of aradio base station according to an embodiment of the present invention;

FIG. 18 is a diagram to show an example of an overall structure of auser terminal according to an embodiment of the present invention; and

FIG. 19 is a diagram to show an example of a functional structure of auser terminal according to an embodiment of the present invention;

DESCRIPTION OF EMBODIMENTS

FIG. 1 show examples of operation modes in a radio communication system(LTE-U) in which LTE is run in unlicensed bands. As shown in FIG. 1, aplurality of scenarios such as carrier aggregation (CA), dualconnectivity (DC) and stand-alone (SA) are possible scenarios to use LTEin unlicensed bands.

FIG. 1A shows a scenario to employ carrier aggregation (CA) by usinglicensed bands and unlicensed bands. CA is a technique to bundle aplurality of frequency blocks (also referred to as “component carriers”(CCs), “cells,” etc.) into a wide band. Each CC has, for example, amaximum 20 MHz bandwidth, so that, when maximum five CCs are bundled, awide band of maximum 100 MHz is provided.

With the example shown in FIG. 1A, a case is illustrated in which amacro cell and/or a small cell to use licensed bands and small cells touse unlicensed bands employ CA. When CA is employed, one radio basestation's scheduler controls the scheduling of a plurality of CCs. Basedon this, CA may be referred to as “intra-base station CA” (intra-eNB CA)as well.

In this case, the small cells to use unlicensed bands may use a carrierthat is used for DL communication only (scenario 1A) or use a TDDcarrier (scenario 1B). The carrier to use for DL communication only isalso referred to as a “supplemental downlink” (SDL). Note that FDDand/or TDD can be used in licensed bands.

Furthermore, a (co-located) structure may be employed here in which alicensed band and an unlicensed band are transmitted and received viaone transmitting/receiving point (for example, a radio base station). Inthis case, the transmitting/receiving point (for example, an LTE/LTE-Ubase station) can communicate with a user terminal by using both thelicensed band and the unlicensed band. Alternatively, it is equallypossible to employ a (non-co-located) structure in which a licensed bandand an unlicensed band are transmitted and received via differenttransmitting/receiving points (for example, one via a radio base stationand the other one via an RRH (Remote Radio Head) that is connected withthe radio base station).

FIG. 1B show a scenario to employ dual connectivity (DC) by using alicensed band and an unlicensed band. DC is the same as CA in bundling aplurality of CCs (or cells) into a wide band. While CA is based on thepremise that CCs (or cells) are connected via ideal backhaul and iscapable of coordinated control, which produces very little delay time,DC presumes cases in which cells are connected via non-ideal backhaul,which produces delay time that is more than negligible.

Consequently, in DC, cells are run by separate base stations, and userterminals communicate by connecting with cells (or CCs) of varyingfrequencies that are run under different base stations. So, when DC isemployed, a plurality of schedulers are provided individually, and thesemultiple schedulers each control the scheduling of one or more cells(CCs) managed thereunder. Based on this, DC may be referred to as“inter-base station CA” (inter-eNB CA). Note that, in DC, carrieraggregation (intra-eNB CA) may be employed per individual scheduler(that is, base station) that is provided.

The example shown in FIG. 1B illustrates a case where a macro cell touse a licensed band and small cells to use unlicensed bands employ DC.In this case, the small cells to use unlicensed bands may use a carrierthat is used for DL communication only (scenario 2A), or use a TDDcarrier (scenario 2B). Note that the macro cell to use a licensed bandcan use FDD and/or TDD.

In the example shown in FIG. 1C, stand-alone (SA) is employed, in whicha cell to run LTE by using an unlicensed band operates alone.Stand-alone here means that communication with terminals is possiblewithout employing CA or DC. In this case, the unlicensed band can be runin a TDD carrier (scenario 3).

FIG. 2 shows an example of an operation mode in a radio communicationsystem (LTE-U) in which LTE is run in an unlicensed band. In theoperation modes of CA and DC shown in FIG. 1A and FIG. 1B, for example,as shown in FIG. 2, it is possible to use a licensed band CC (macrocell) as a primary cell (PCell) and use an unlicensed band CC (smallcell) as a secondary cell (SCell). Here, the primary cell (PCell) refersto the cell that manages RRC connection, handover and so on when CA/DCis used, and is also a cell that requires UL communication such as dataand feedback signals from user terminals. The primary cell is alwaysconfigured in the uplink and the downlink. A secondary cell (SCell) isanother cell that is configured in addition to the primary cell whenCA/DC is employed. Secondary cells may be configured in the downlinkalone, or may be configured in both the uplink and the downlink at thesame time.

Note that, as shown in above FIG. 1A (CA) and FIG. 1B (DC), a mode topresume the presence of licensed-band LTE (licensed LTE) when runningLTE-U is referred to as “LAA” (Licensed-Assisted Access) or “LAA-LTE.Note that systems that run LTE/LTE-A in unlicensed bands may becollectively referred to as “LAA,” “LTE-U,” “U-LTE” and so on.

In LAA, licensed band LTE and unlicensed band LTE are coordinated so asto allow communication with user terminals. LAA may assume a structure,in which a transmission point to use a licensed band (for example, aradio base station) and a transmission point to use an unlicensed band,when being a distance apart, are connected via a backhaul link (forexample, optical fiber, the X2 interface and so on).

Now, existing LTE presumes operations in licensed bands, and thereforeeach operator is allocated a different frequency band. However, unlike alicensed band, an unlicensed band is not limited to use by a specificprovider. Consequently, there is a possibility that the frequency bandwhich a given operator uses in LTE-U overlaps the frequency band whichanother operator uses in an LAA system, a Wi-Fi system and so on.

When run in an unlicensed band, LTE may be carried out without evensynchronization, coordination and/or cooperation between differentoperators and/or non-operators. In this case, a plurality of operatorsand/or systems share and use the same frequency in the unlicensed band,and therefore there is a threat of producing cross-interference.

So, in a Wi-Fi system that runs in an unlicensed band, resourceallocation is carried out so that, in a given period, all bands are usedfor a specific user. Consequently, in Wi-Fi, in order to preventtransmitting signals from colliding each other between user terminals,access points and so on, carrier sense multiple access/collisionavoidance (CSMA/CA), which is based on the mechanism of LBT (ListenBefore Talk), is employed. To be more specific, for example, eachtransmission point (TP), access point (AP), Wi-Fi terminal (STA:Station) and so on perform “listening” (CCA: Clear Channel Assessment)before carrying out transmission, and carries out transmission only whenthere is no signal beyond a predetermined level.

In view of the above, LBT is expected to be required even in LTE/LTE-Asystems (for example, an LAA system) to be run in unlicensed bands. Byintroducing LBT in LAA systems, it becomes possible to preventinterference between LAA and Wi-Fi. Also, it is possible to preventinterference between LAA systems. Even when user terminals that can beconnected are controlled independently for every operator that runs anLAA system, it is possible to reduce interference without learning thedetails of the control for each operator, by means of LBT.

In LTE-systems to use LBT, an LTE-U base station and/or a user terminalperform listening (LBT) before transmitting signals in an unlicensedband cell, and, if no signal from other systems (for example, Wi-Fi)and/or other LAA transmission points is detected, the LTE-U base stationand/or the user terminal communicate in the unlicensed band. Forexample, if received power that is equal to or lower than apredetermined threshold is measured in LBT, the LTE-U base stationand/or the user terminal judge that the channel is in an idle state(LBT_idle) and carriers out transmission. When a “channel is in an idlestate,” this means that, in other words, the channel is not occupied bya certain system, and it is equally possible to say that the channel isclear, the channel is free and so on.

On the other hand, if, as a result of listening, signals from othersystems and/or other LAA transmission points are detected, processessuch as (1) making a transition to another carrier by way of DFS(Dynamic Frequency Selection), (2) applying transmission power control(TPC), or (3) holding (stopping) transmission may be carried out. Forexample, when the received power that is measured in LBT exceeds apredetermined threshold, the LTE-U base station and/or the user terminaljudge that the channel is in a busy state (LBT_busy) and do not carryout transmission. In the event of LBT_busy, this channel becomesavailable for use after a predetermined backoff time is over. Note thatthe method of judging whether a channel is in an idle state/busy statebased on LBT is by no means limited to this.

FIG. 3 provide diagrams to show operating agents in LBT in a system inwhich LTE/LTE-A is run in an unlicensed band. In FIG. 3, a radio basestation (eNB) to form an unlicensed band cell, a user terminal (UE), andthe downlink (DL)/uplink (UL) between these are shown. In the unlicensedband cell, listening (LBT) is carried out before a signal istransmitted, to check whether transmission points of other systems (forexample, Wi-Fi) or other LAA (LTE-U) transmission points are engaged incommunication. FIG. 3A shows an example in which the eNB carries out LBTwith respect to both DL and UL. In this case, after the eNB judges thatthe channel is in the clear state based on LBT, the eNB reports apredetermined signal (for example, a UL grant) to the UE, so that the UEcan carry out UL transmission. On the other hand, FIG. 3B shows anexample of carrying out LBT on the transmitting side. In this case, LBTis carried out by the eNB in the event of DL transmission and by the UEin the event of UL transmission. Here, the LBT which the user terminalperforms with respect to UL may be referred to as “UL-LBT.”

The general idea of UL-LBT is that the state of unlicensed bandinterference in the user terminal can be learned adequately. However, noframe configuration that is suitable for UL-LBT has been proposed sofar. In particular, unless the subframes for carrying out LBT sensingand/or the time of length of sensing are configured adequately, it maynot be possible to adequately prevent producing interference with ULsignals.

So, the present inventors have come up with the idea of providingadequate LBT-based sensing configurations (sensing patterns) for whenuser terminals carry out LBT in a system that runs LTE/LTE-A in anunlicensed band. To be more specific, the present inventors have come upwith the idea of carrying out LBT by using predetermined subframes assensing subframes based on the sensing patterns. Furthermore, thepresent inventors have come up with the idea of adequately configuringthe length of each period (LBT-executing period, and/or others) includedin sensing subframes.

According to the present invention, the subframes to carry out LBTsensing and/or the time length of sensing can be configured adequately,so that it is possible to prevent producing interference with UL signalsin an LTE system in an unlicensed band.

Now, embodiments of the present invention will be described below indetail with reference to the accompanying drawings. Note that, althoughexamples will be illustrated with the following description where LBT isused in an LTE-U operation mode (LAA) to presume the presence oflicensed bands, the embodiments are by no means limited to this. Also,although structures will be presumed in which user terminals carry outLBT and radio base stations do not carry out LBT, the radio basestations may be capable of carrying out LBT as well.

FIG. 4 is a diagram to show examples of frame configurations for LBT ina system in which LTE/LTE-A is run in an unlicensed band. One subframe(1 ms) is comprised of two slots, and one slot is equivalent to 0.5 ms.Also, one slot is comprised of seven OFDM symbols (six symbols when anextended cyclic prefix is used), and one OFDM symbol is equivalent to66.7 μs+T_(CP) (T_(CP): cyclic prefix length).

Also, the letters assigned to each subframe represents the types ofsubframes, where “D” stands for downlink (DL) subframes, “U” stands foruplink (UL) subframes, and “S” stands for special subframes or subframesin which LBT-based sensing is carried out (also referred to as “sensingsubframes”). Note that the subframe configuration shown in FIG. 4 (theorder in which D, U and S are placed) is one example, and this is by nomeans limiting.

The special subframe according to conventional (Rel. 11) TDD UL/DLconfigurations is comprised of a DwPTS (Downlink Pilot Time Slot), a GP(Guard Period) and a UpPTS (Uplink Pilot Time Slot). On the other hand,the sensing subframe according to the present invention is comprised ofan LBT (LBT period), a GP (Guard Period) and a Report (report period).That is, the sensing subframe configuration according to the presentinvention is similar to the conventional special subframe configuration,so that it is possible to reduce the cost of implementing userterminals.

The LBT period is used to allow a user terminal to detect channelstates. To be more specific, the user terminal carries out listening(LBT) in the LBT period. Here, unlike special subframes, the userterminal does not have to try receiving and demodulating/decoding thePDSCH (Physical Downlink Shared Channel) in sensing subframes.

The GP is used as a guard period for allowing the user terminal toswitch from listening to sending a report. Also, depending on the lengthof the GP, the serving cell's cell coverage radius is determined. Tomake the cell radius bigger, a relatively long GP is required. On theother hand, when the cell radius is small, a short GP suffices. That is,the GP is a guard period for switching between transmission andreception.

The report period is a period to transmit feedback information forcarrying out transmission in UL subframes following sensing subframes.The feedback information is used to allow the user terminal to transmitthe PUSCH and radio base stations to receive this PUSCH. That is, thisis useful information in PUSCH transmission. Candidates of this usefulinformation include, for example, a scheduling request (SR)/randomaccess preamble (RAP) and so on. With these, it becomes possible torequest UL grants and transmit data after sensing. Also, othercandidates of useful information include parameters related to thedemodulation of the PUSCH, such as resource blocks (RBs), MCS(Modulation and Coding Scheme), and so on. By using these, it ispossible to carry out data transmission after sensing without using ULgrants.

FIG. 5 is a flowchart to show an example of UL-LBT processes in a userterminal according to the present invention. First, a user terminalacquires the sensing pattern (step S1). As will be described later, theuser terminal acquires the sensing pattern via an implicit or explicitreport, or calculates and acquires the sensing pattern based onpredetermined rules.

Here, the sensing pattern refers to information about the configurationof LBT-based sensing. In other words, the sensing pattern is informationabout the timing in which the user terminal performs LBT. The sensingpattern is, for example, formed by combining sensing subframes and thecycle of performing sensing (the cycle of sensing subframes, alsoreferred to as the “sensing period”). The sensing pattern may beexpressed as: (the subframes to be sensing subframes, the sensingperiod). For example, the sensing pattern when sensing is performed inarbitrary subframes every 1 ms may be expressed as: (Arbitrarysubframes, 1 ms). Note that the sensing pattern is by no means limitedto the above format.

The user terminal judges whether or not the current subframe is asensing subframe based on the sensing pattern (step S2). When thecurrent subframe is not a sensing subframe (step S2: NO), the userterminal carries out step S2 again in the next subframe.

When the current subframe is a sensing subframe (step S2: YES), the userterminal executes UL-LBT (step S3). Then, based on the result of UL-LBT,the user terminal judges whether or not the channel is free (step S4).When judging that the channel not free (step S4: NO), the user terminalcarries out step S2 again in the next subframe. Note that, when thesensing pattern is calculated in the user terminal in step S1 and thechannel is judged not free, the user terminal may carry out step S1again (the chained line in FIG. 5).

When judging that the channel is free (step S4: YES), the user terminalcarries out UL transmission in the following UL subframe (step S5).

The present invention primarily relates to steps S1 to S3 in FIG. 5. Inparticular, the method of acquiring the sensing pattern in step S1 willbe described in detail with reference to a first and a secondembodiment.

First Embodiment

According to the first embodiment, sensing patterns are associated withTDD UL/DL configurations. In other words, the first embodiment isapplicable to cases where an unlicensed band to perform LBT is a TDDcarrier.

FIG. 6 is a diagram to show examples of associations of TDD UL/DLconfigurations and sensing patterns. In FIG. 6, “Config.” indicates TDDUL/DL configurations, and “Subframe index” indicates the types ofsubframes corresponding to the UL/DL configurations. Here, “D” standsfor downlink (DL) subframes, “U” stands for uplink (UL) subframes and“S” stands for special subframes or sensing subframes.

In the example of FIG. 6, the special subframes are all used as sensingsubframes. The special subframe can be seen as DL subframes, so that, inother words, in FIG. 6, the DL subframes that neighbor (that immediatelyprecede) UL subframes are configured as sensing subframes. Consequently,in UL/DL configurations {0, 1, 2, 6}, the sensing period is 5 ms, and,in UL/DL configurations 3 to 5, the sensing period is 10 ms. Also, inUL/DL configurations 0 to 6, the number of UL subframes that followafter the sensing subframes is one to three, so that thechannel-occupying time to be determined based on LBT results is 1 to 3ms.

A radio base station reports the sensing pattern to a user terminal byusing higher layer signaling (for example, RRC signaling), broadcastinformation (for example, SIB 1) and so on. The sensing pattern may bereported with the UL/DL configuration, or, if the sensing pattern isassociated with a UL/DL configuration in advance, the UL/DLconfiguration may be reported so as to report the sensing patternimplicitly. For example, in the event of Config. 2, (Special subframes,5 ms) may be reported explicitly as the sensing pattern, or, whenConfig. 2 is reported as the UL/DL configuration, the user terminal mayinterpret this as an implicit report of (Special subframes, 5 ms). Notethat for the UL/DL configurations, configurations that are differentfrom UL/DL configurations 0 to 6 shown in FIG. 6 may be used, and, inthat case, the DL subframes that neighbor (that immediately precede) ULsubframes may be made sensing subframes.

Next, methods of configuring the length of each period (LBT, GP andReport) included in sensing subframes will be described. In method 1,conventional (LTE Rel. 11) special subframe configurations are re-usedas sensing subframe configurations. To be more specific, according tomethod 1, the lengths of DwPTS, GP and UpPTS in special subframes areused as the lengths of LBT, GP and Report in sensing subframes,respectively.

FIG. 7 is a diagram to show examples of special subframe configurationsin TDD. “Special subframe config.” indicates special subframeconfigurations. Also, the lengths of DwPTS, GP and UpPTS are given insymbol units. For example, when special subframe configuration 0 isselected as the sensing subframe configuration, the lengths of LBT, GPand Report in sensing subframes are three, ten and one OFDM symbol,respectively. Note that the special subframe configurations are notlimited to configurations 0 to 9 shown in FIG. 7.

Each special subframe configuration determines the lengths of DwPTS, GPand UpPTS. Also, each configuration is provided for the case where thenormal cyclic prefix is used (the symbol duration of one subframe is14), and the case where an extended cyclic prefix is used (the symbolduration of one subframe is 12). Note that each configuration has onlyto define at least two parameters, and one parameter may be removed. Forexample, if only DwPTS and UpPTS are defined, GP does not have to bedefined. In this case, the user terminal can judge the length of GPbased on the symbol duration, DwPTS and UpPTS.

Note that, from the perspective of improving the accuracy of LBTsensing, it is preferable to make the time of GP shorter—to be morespecific, three symbols or shorter. That is, it is preferable to selectsensing subframe configurations from the special subframe configurationsof {2, 3, 4, 6, 7, 8} (when the normal cyclic prefix is used) or {1, 2,3, 5, 6} (when an extended cyclic prefix is used).

In method 2, new sensing subframe configurations are defined. Accordingto method 2, the lengths of LBT, GP and Report in sensing subframes canbe configured without relying upon the lengths of DwPTS, GP and UpPTS inspecial subframes, respectively.

FIG. 8 is a diagram to show examples of sensing subframe configurationin TDD. “Sensing subframe config.” indicates sensing subframeconfigurations. Also, the lengths of DwPTS, GP and UpPTS are given insymbol units. Note that the sensing subframe configurations are notlimited to configurations 0 to 9 shown in FIG. 8. Also, the sensingsubframe configurations may use different lengths of LBTs, GPs andReports from those shown in FIG. 8.

As clear from the comparison of FIG. 8 and FIG. 7, it is preferable tostructure the sensing subframe configurations to include many GPs ofsmaller values than the GPs in conventional (Rel. 11) special subframeconfigurations. By this means, it becomes possible to configure guardperiods that are more suitable for small cells having relatively smallcoverage radii.

Also, as clear from the comparison of FIG. 8 and FIG. 7, it ispreferable to structure the sensing subframe configurations to includemany Reports of greater values than the UpPTSs in conventional (Rel. 11)special subframe configurations. By this means, the report period isextended, and it becomes possible to transmit many pieces of usefulinformation (for example, NAV (Network Allocation Vector), BSR (BufferStatus Report), etc.). Also, when a plurality of different userterminals carry out transmissions in the report period in the samesensing subframe, it becomes possible to allocate differenttime/frequency/code resources between user terminals, so that thepossibility of collisions of transmitting signals can be reduced.

Information about the sensing subframe configuration that is applied maybe reported to the user terminal through higher layer signaling (forexample, RRC signaling) and/or broadcast information (for example, SIB1). Here, when a plurality of sensing subframes are present in a radioframe, each sensing subframe may use a different sensing subframeconfiguration. Also, in the event of above method 1, the specialsubframe configuration and the sensing subframe configuration to beapplied to a radio frame may be selected to be different.

Note that, although FIG. 6 shows an example in which all the specialsubframes are used as sensing subframes, this is by no means limiting.For example, a structure may be used in which, when a plurality ofspecial subframes are present in a radio frame, part of the specialsubframes is used as sensing subframes. In this structure, the specialsubframes that are not used as sensing subframes can be used as DLsubframes, so that it is possible to maintain a relatively short sensingperiod (for example, ten subframes or shorter), and, furthermore, reducethe decrease of DL throughput.

FIG. 9 is a diagram to show examples of associations of TDD UL/DLconfigurations and sensing patterns. Unlike the examples of FIG. 6, inthe examples of FIG. 9, in UL/DL configurations {0, 1, 2, 6}, in which aplurality of special subframes are included in one frame, the specialsubframe of subframe 1 is made a sensing subframe, and the specialsubframe of subframe 6 is used as a special subframe on an as-is basis.Consequently, in UL/DL configurations 0 to 6, the sensing period is 10ms.

Note that the allocation rule as to which special subframes are used assensing subframes is by no means limited to this. For example, in thecase of FIG. 9, it is possible to employ a structure in which, in UL/DLconfigurations {0, 1, 2, 6}, the special subframe of subframe 6 is usedas a sensing subframe, and the special subframe of subframe 1 is used asa special subframes on an as-is basis. Also, it is possible to employ astructure to use different special subframes as sensing subframes on aper radio frame basis.

Also, it is possible to use a structure in which the sensing period islonger than ten subframes, and in which a radio frame including nosensing subframes is present. For example, the sensing period may bemade 20 ms, 40 ms and 80 ms. According to this structure, it is possibleto use special subframes that are not used as sensing subframes as DLsubframes, so that it is possible to maintain executing sensing in apredetermine period, and, furthermore, reduce the decrease of DLthroughput even more. The sensing period may be reported to the userterminal via higher layer signaling (for example, RRC signaling) and/orbroadcast information (for example, SIB 1).

Second Embodiment

With the second embodiment, the sensing patterns are not associated withTDD UL/DL configurations. In this case, the user terminal implicitlyjudges the sensing pattern to use, or uses sensing patterns that arereported explicitly.

When the user terminal judges the sensing pattern implicitly, the userterminal carries out sensing if predetermined conditions are fulfilled.In this case, the user terminal calculates the sensing pattern inaccordance with predetermined rules. FIG. 10 provide diagrams to showexamples of sensing patterns that are configured implicitly. Forexample, as shown in FIG. 10A, a structure may be employed, in which thesensing period is one subframe, and in which sensing is always carriedout when there is data to transmit. In this case, the sensing pattern is(Arbitrary subframes, 1 ms). In the example of FIG. 10A, the sensingresults in subframes 0 and 1 are “busy” and the result in subframe 2 is“free,” so that the user terminal can execute transmission in, forexample, subframe 3. In this way, although a structure to executesensing on a per subframe basis makes the time to wait for sensing shortand enables transmission with low delays, sensing is performed with highfrequency, and this results in increased power consumption.

Also, when there is data to transmit, a structure may be employed inwhich the sensing period is changed depending on the number of timessensing is performed in order to transmit this data. For example, whenthe sensing result is “busy,” the user terminal may change the sensingperiod by determining the next sensing subframe based on following table1:

TABLE 1 Sensing period Sensing period (ms) i ≦ 5 (SF_(current) +2^(5 − i)) mod 10 2^(5 − i) i > 5 (SF_(current) + 1) mod 10 1

Here, i is the number of times sensing is performed (the number of timesto wait for transmission), and SF_(current) is the current subframe.

In the example of FIG. 10B, the result of sensing in subframe 0 is“busy,” and, at this time, i=3 and SF_(current)=0. So, the user terminaldetermines the next sensing subframe=(0+2⁵⁻³)mod 10=4 based on table 1.

The result of sensing in subframe 4 is “busy,” and, at this time, i=4and SF_(current)=4. So, the user terminal determines the next sensingsubframe=(4+2⁵⁻⁴)mod 10=6 based on table 1.

The result of sensing in subframe 6 is “busy,” and, at this time, i=5and SF_(current)=6. So, the user terminal determines the next sensingsubframe=(6+2⁵⁻⁵)mod 10=7 based on table 1.

The result of sensing in subframe 7 is “busy,” and, at this time, i=6and SF_(current)=7. So, the user terminal determines the next sensingsubframe=(7+1)mod 10=8 based on table 1.

The result of sensing in subframe 8 is “free,” so that the user terminalcan start the transmission process. In this way, a structure to changethe sensing period depending on the number of times to try sensing makespossible a trade-off between delay and power consumption.

Note that the implicit sensing patterns are not limited to these. Forexample, a structure may be employed here in which sensing is carriedout for every several subframes, instead of carrying out sensing on aper subframe basis. Also, a structure may be employed in which thesensing period is made long depending the number of times of sensing.

Next, a case will be described in which the user terminal uses sensingpatterns that are reported explicitly. FIG. 11 is a diagram to showexamples of sensing patterns that are reported explicitly. “Sensingpattern index” indicates the indices of sensing patterns. FIG. 11 showssensing patterns that presume periodic sensing, and one sensing patternis associated with a sensing subframe start offset (that is, the indexof the minimum sensing subframe in one frame) and a sensing period. Forexample, referring to FIG. 11, when the sensing pattern index is 0, thesensing subframe is 0, and the sensing period is 6.

The sensing patterns may be cell-specific. In this case, the radio basestations forming each cell report cell-specific sensing patterns to theuser terminals in each cell by using broadcast information (for example,SIB 1). Also, the sensing patterns may be user terminal-specific. Inthis case, the radio base stations report user terminal-specific sensingpatterns to the user terminals by using higher layer signaling (forexample, RRC signaling).

FIG. 12 provide diagrams to show examples in which cell-specific sensingpatterns are reported explicitly. In the example of FIG. 12, UE 1 isconnected with unlicensed band cell 1, and UE 2 is connected withunlicensed band cell 2. Cell 1 reports sensing pattern 0 (see FIG. 11),which is the subject cell's sensing pattern, to UE 1, which is a servinguser terminal, and cell 2 reports sensing pattern 1 (see FIG. 11), whichis the subject cell's sensing pattern, to UE 2, which is a serving userterminal. Note that a structure may be employed here in which radio basestations (cells) report the sensing patterns used in the subject cellsto each other, or a structure may be employed in which radio basestations select and use sensing patterns that are from those of othercells. By so doing, even when the coverage areas of a plurality of cellsoverlap, it is possible to prevent collisions of UL transmissions afterLBT by using mutually varying sensing patterns.

FIG. 13 provide diagrams to show examples of cases where userterminal-specific sensing patterns are reported explicitly. In theexample of FIG. 13, UE 1 and UE 2 are connected with licensed band cell0 and unlicensed band cell 1. Cell 0 reports, to UE 1 and UE 2, whichare serving user terminals, sensing patterns 0 and 1 (see FIG. 11),which are the sensing patterns of these. Note that it is equallypossible to employ a structure to report user terminal-specific sensingpatterns from the unlicensed band cell.

Note that it is equally possible to use a structure to directly reportthe start offset of sensing subframes, the sensing period and so on,instead of reporting sensing patterns. According to this structure, theuser terminals are not limited to combinations that are determined basedon sensing patterns, and are able to execute sensing adequately.

According to the second embodiment, the sensing subframe configurationsmay use configurations to include an LBT, a GP and a Report. In thiscase, the user terminal may, as has been described with the firstembodiment, decide the length of each period in sensing subframes basedon the special subframe configurations in TDD, newly defined sensingsubframe configurations and so on. Also, the sensing subframeconfigurations of the second embodiment are by no means limited toconfigurations including an LBT, a GP and a Report. For example, it ispossible to make the whole of a sensing subframe the LBT time.

The sensing subframe start offset, the sensing period and the sensingsubframe configuration may be reported on a per cell basis, by usingbroadcast information (for example, SIB 1), or may be reported on a peruser terminal basis by using higher layer signaling (for example, RRCsignaling). It is preferable to report these on a per cell basis if thesensing patterns are cell-specific, or on a per user terminal basis ifthe sensing patterns are user terminal-specific.

Note that, according to the first and second embodiments, the sensingpattern, the sensing period, the LBT sensing time and so on aredetermined so as to fulfill predetermined LBT-related restrictions (forexample, restrictions by the country, region and so on). To be morespecific, the sensing time, the channel-occupying time and so on aredetermined so as to allow flexible and even use of bands with othersystems that use unlicensed bands. For example, in Europe, thechannel-occupying time is required to be within 1 ms at a minimum and 10ms at a maximum.

Third Embodiment

Methods of configuring sensing subframes semi-statically have beendescribed with the above first and second embodiments. Since theseembodiments presume using sensing subframes in UL-LBT, for terminalsthat have little (or no) UL data, it is a waste to execute LBT insensing subframes. In many cases, traffic tends to be concentrated inDL, and therefore, for example, using 20% of the resources for UL-LBT asshown with the structure of Config. 2 in FIG. 6 is a significant waste.

From this perspective, the present inventors have furthermore come upwith the idea of switching sensing subframes in accordance with traffic.To be more specific, the present inventors have arrived at using sensingsubframes as conventional special subframes when there is DL traffic andas sensing subframes when there is UL traffic. By this means, it becomespossible to use radio resources more effectively.

According to a third embodiment of the present invention, whether to useeach sensing subframe as a sensing subframe or as a special subframe isdecided. FIG. 14 is a flowchart to show an example of sensing subframeswitching processes in the third embodiment.

First, a user terminal judges whether or not the current subframe is asensing subframe (step S11). If the current subframe is not a sensingsubframe (step S11: NO), the user terminal waits until the nextsubframe, and carries out step S11 again.

If the current subframe is a sensing subframe (step S11: YES), the userterminal first reads the PCFICH (Physical Control Format IndicatorChannel), and, based on the PCFICH, tries to receive the PDCCH (PhysicalDownlink Control Channel) in a predetermined OFDM symbol period (forexample, in a period of one to two OFDM symbols) (step S12).Alternatively, in step S12, the user terminal may skip receiving thePCFICH, and try receiving the PDCCH in a predetermined OFDM symbolperiod (for example, in a period of one to two OFDM symbols) that isconfigured in advance by higher layer signaling (for example, RRCsignaling and so on).

The user terminal judges whether or not UL data is held in the buffer(step S13). If the user terminal judges that UL data is held (step S13:YES), as a result of step S12, the user terminal further judges whetheror not a DL assignment to designate the PDSCH for the subject terminalis detected (step S14). When judging that a DL assignment has beendetected (step S14: YES), the user terminal performs one of thefollowing (step S15):

(Alt. 1) the user terminal identifies the current subframe as a specialsubframe, pends UL-LBT (pending) and executes DL reception; and

(Alt. 2) the user terminal identifies the current subframe a sensingsubframe, gives up DL reception, and performs UL-LBT. Here, in DLreception, the user terminal receives and demodulates the PDSCH in thesame way as with DwPTS in conventional special subframes. Note that,when the user terminal performs Alt. 2, it is preferable to use astructure to transmit NACK in a predetermined timing so as to let theradio base station know that the user terminal has given up DLreception.

In above Alt. 1, it is possible to transmit and receive DL, where thetraffic tends to be heavy, so that it is possible to improve userthroughput. Although UL, which tends to have light traffic, is pended,and the delays of UL grow, this is not particularly a problem becausetransmission can be carried out in future transmitting/receivingopportunities. In above-described Alt. 2, UL data to have greater delaysthan DL can be transmitted/received preferentially, so that it ispossible to improve the speed the user experiences. Although DLreception fails in this subframe, this is not particularly a problem,because a DL assignment has been detected, so that, if only a NACK canbe transmitted in a predetermined timing, a retransmission can be madein a future transmitting/receiving opportunity.

Meanwhile, if the user terminal judges that no DL assignment has beendetected (step S14: NO), the user terminal identifies the currentsubframe as a sensing subframe, and executes UL-LBT (step S16).

Also, when the user terminal judges that no UL data is held (step S13:NO), the user terminal furthermore judges whether or not a DL assignmentto designate the PDSCH for the subject terminal has been detected (stepS17). When the user terminal judges that a DL assignment has beendetected (step S17: YES), the user terminal identifies the currentsubframe as a special subframe, and executes DL reception (step S18).

Meanwhile, although a structure is used in the example of FIG. 14 inwhich the user terminal does nothing (does not carry out transmission,reception or sensing) when judging that no DL assignment has beendetected (step S17: NO), this is by no means limiting. For example, theuser terminal may identify the current subframe as a sensing subframeand execute UL-LBT.

Note that, in above step S15, it is possible to switch between andperform the operations of Alt. 1 and Alt. 2 depending on whether or notthe UL data that is held in the buffer is control information. Forexample, when there is UL data that includes control information, theuser terminal gives up DL reception and executes UL-LBT, and, otherwise,pends UL-LBT and prioritizes DL reception. By this means, the userterminal becomes capable of transmitting control information, which isimportant in communication, as quickly as possible.

Also, it is equally possible to use a structure in which UL-LBT iscarried out in above steps S15 and S16 if a UL grant to command a PUSCHtransmission is detected upon the reception of the PDCCH in step S12.

Also, although, in accordance with the first and second embodiments, theabove-described flow presumes a case where sensing subframes areconfigured in advance, this is by no means limiting. For example, it isequally possible to use a structure in which, when sensing subframes arenot configured in advance, the user terminal judges whether or not thecurrent subframe is a special subframe in step S11, and performsprocesses of step S12 and later steps when the current subframe is aspecial subframe.

As described above, according to the third embodiment, it is possible touse a predetermined subframe as a sensing subframe and/or as a specialsubframe depending on uplink/downlink traffic, so that radio resourcescan be used more flexibly. Also, by executing UE operations to tryreceiving control signals in the first several symbols of this subframe,a radio base station can transmit, to a user terminal, a DL assignmentto command receiving the PDSCH in the event of a special subframe, ortransmit a UL grant to command transmitting the PUSCH in the event of asensing subframe.

(Structure of Radio Communication System)

Now, the structure of the radio communication system according to oneembodiment of the present invention will be described below. In thisradio communication system, the above-described radio communicationmethods according to the first to third examples are employed. Note thatthe above-described radio communication methods of the first to thirdexamples may be applied individually or may be applied in combination.

FIG. 15 is a diagram to show an example of a schematic structure of aradio communication system according to the present embodiment. Notethat the radio communication system shown in FIG. 15 is a system toincorporate, for example, an LTE system, super 3G and LTE-A system. Thisradio communication system can adopt carrier aggregation (CA) and/ordual connectivity (DC) to group a plurality of fundamental frequencyblocks (component carriers) into one, where the LTE system bandwidthconstitutes one unit. Also, the radio communication system shown in FIG.15 has a radio base station (for example, an LTE-U base station) that iscapable of using unlicensed bands. Note that this radio communicationsystem may be referred to as “IMT-Advanced,” or may be referred to as“4G” or “FRA” (Future Radio Access).

The radio communication system 1 shown in FIG. 15 includes a radio basestation 11 that forms a macro cell C1, and radio base stations 12 a and12 b that form small cells C2, which are placed within the macro cell C1and which are narrower than the macro cell C1. Also, the user terminals20 are placed in the macro cell C1 and in each small cell C2. Forexample, a mode may be possible in which the macro cell C1 is used in alicensed band and the small cells C2 are used in unlicensed bands(LTE-U). Also, a mode may be also possible in which part of the smallcells is used in a licensed band and the rest of the small cells areused in unlicensed bands.

The user terminals 20 can connect with both the radio base station 11and the radio base stations 12. The user terminals 20 may use the macrocell C1 and the small cells C2, which use different frequencies, at thesame time, by means of CA or DC. For example, it is possible to transmitassist information (for example, the DL signal configuration) related toa radio base station 12 (which is, for example, an LTE-U base station)that uses an unlicensed band, from the radio base station 11 to use alicensed band to the user terminals 20. Also, a structure may beemployed here in which, when CA is used between a licensed band and anunlicensed band, one radio base station (for example, the radio basestation 11) controls the scheduling of licensed band cells andunlicensed band cells.

Note that it is equally possible to use a structure in which the userterminals 20 connect with the radio base stations 12, instead ofconnecting with the radio base station 11. For example, it is possibleto use a structure in which a radio base station 12 to use an unlicensedband connects with the user terminals 20 in stand-alone. In this case,the radio base station 12 controls the scheduling of unlicensed bandcells.

Between the user terminals 20 and the radio base station 11,communication is carried out using a carrier of a relatively lowfrequency band (for example, 2 GHz) and a narrow bandwidth (referred toas, for example, “existing carrier,” “legacy carrier” and so on).Meanwhile, between the user terminals 20 and the radio base stations 12,a carrier of a relatively high frequency band (for example, 3.5 GHz andso on) and a wide bandwidth may be used, or the same carrier as thatused in the radio base station 11 may be used. Between the radio basestation 11 and the radio base stations 12 (or between two radio basestations 12) wire connection (optical fiber, the X2 interface, etc.) orradio connection may be established.

The radio base station 11 and the radio base stations 12 are eachconnected with a higher station apparatus 30, and are connected with acore network 40 via the higher station apparatus 30. Note that thehigher station apparatus 30 may be, for example, an access gatewayapparatus, a radio network controller (RNC), a mobility managemententity (MME) and so on, but is by no means limited to these. Also, eachradio base station 12 may be connected with the higher station apparatus30 via the radio base station 11.

Note that the radio base station 11 is a radio base station having arelatively wide coverage, and may be referred to as a “macro basestation,” a “central node,” an “eNB” (eNodeB), a “transmitting/receivingpoint” and so on. Also, the radio base stations 12 are radio basestations having local coverages, and may be referred to as “small basestations,” “micro base stations,” “pico base stations,” “femto basestations,” “HeNBs” (Home eNodeBs), “RRHs” (Remote Radio Heads),“transmitting/receiving points” and so on. Hereinafter the radio basestations 11 and 12 will be collectively referred to as a “radio basestation 10,” unless specified otherwise. The user terminals 20 areterminals to support various communication schemes such as LTE, LTE-Aand so on, and may be either mobile communication terminals orstationary communication terminals.

In the radio communication system, as radio access schemes, OFDMA(Orthogonal Frequency Division Multiple Access) is applied to thedownlink, and SC-FDMA (Single-Carrier Frequency Division MultipleAccess) is applied to the uplink. OFDMA is a multi-carrier transmissionscheme to perform communication by dividing a frequency band into aplurality of narrow frequency bands (subcarriers) and mapping data toeach subcarrier. SC-FDMA is a single-carrier transmission scheme tomitigate interference between terminals by dividing the system band intobands formed with one or continuous resource blocks per terminal, andallowing a plurality of terminals to use mutually different bands. Notethat the uplink and downlink radio access schemes are by no limited tocombinations of these.

In the radio communication system 1, a downlink shared channel (PDSCH:Physical Downlink Shared CHannel), which is used by each user terminal20 on a shared basis, a broadcast channel (PBCH: Physical BroadcastChannel) and downlink L1/L2 control channels are used as downlinkchannels. User data, higher layer control information and predeterminedSIBs (System Information Blocks) are communicated in the PDSCH. Also,MIBs (Master Information Block) and so on are communicated in the PBCH.

The downlink L1/L2 control channels include a PDCCH (Physical DownlinkControl Channel), an EPDCCH (Enhanced Physical Downlink ControlChannel), a PCFICH (Physical Control Format Indicator Channel), a PHICH(Physical Hybrid-ARQ Indicator Channel) and so on. By the PDCCH,downlink control information (DCI), including PDSCH and PUSCH schedulinginformation, and so on communicated. The number of OFDM symbols to usefor the PDCCH is transmitted by the PCFICH. HARQ deliveryacknowledgement signals (ACKs/NACKs) in response to the PUSCH arecommunicated by the PHICH. The EPDCCH is frequency-division-multiplexedwith the PDSCH (downlink shared data channel), and may be used tocommunicate DCI, like the PDCCH.

Also, in the radio communication system 1, an uplink shared channel(PUSCH: Physical Uplink Shared Channel), which is used by each userterminal 20 on a shared basis, an uplink control channel (PUCCH:Physical Uplink Control Channel), a random access channel (PRACH:Physical Random Access Channel) and so on are used as uplink channels.User data and higher layer control information are communicated by thePUSCH. Also, downlink radio quality information (CQI: Channel QualityIndicator), delivery acknowledgement signals and so on are communicatedby the PUCCH. Random access preambles (RA preambles) for establishingconnections with cells are communicated by the PRACH.

FIG. 16 is a diagram to show an example of an overall structure of aradio base station 10 (which may be either a radio base station 11 or12) according to the present embodiment. The radio base station 10 has aplurality of transmitting/receiving antennas 101 for MIMO communication,amplifying sections 102, transmitting/receiving sections 103, a basebandsignal processing section 104, a call processing section 105 and acommunication path interface 106. Note that the transmitting/receivingsections 103 may be comprised of transmitting sections and receivingsections.

User data to be transmitted from the radio base station 10 to a userterminal 20 on the downlink is input from the higher station apparatus30 to the baseband signal processing section 104, via the communicationpath interface 106.

Given the user data, the baseband signal processing section 104 performstransmission processes such as a PDCP (Packet Data Convergence Protocol)layer process, division and coupling of user data, RLC (Radio LinkControl) layer transmission processes such as an RLC retransmissioncontrol, MAC (Medium Access Control) retransmission control (forexample, an HARQ (Hybrid Automatic Repeat reQuest) transmissionprocess), scheduling, transport format selection, channel coding, aninverse fast Fourier transform (IFFT) process and a precoding process,and the result is forwarded to each transmitting/receiving section 103.Furthermore, downlink control signals are also subjected to transmissionprocesses such as channel coding and an inverse fast Fourier transform,and forwarded to each transmitting/receiving section 103.

Also, the baseband signal processing section 104 reports, to the userterminal 20, control information for allowing communication in the cell,through higher layer signaling (for example, RRC signaling, broadcastinformation and so on). The information for allowing communication inthe cell includes, for example, the system bandwidth on the uplink, thesystem bandwidth on the downlink, and so on.

Also, assist information (for example, DL TPC information and so on)that relates to unlicensed band communication may be reported from aradio base station (for example, the radio base station 11) to the userterminal 20 in a licensed band.

Each transmitting/receiving section 103 converts baseband signals thatare pre-coded and output from the baseband signal processing section 104on a per antenna basis, into a radio frequency band. The radio frequencysignals having been subjected to frequency conversion in thetransmitting/receiving sections 103 are amplified in the amplifyingsections 102, and transmitted from the transmitting/receiving antennas101. For the transmitting/receiving sections 103,transmitters/receivers, transmitting/receiving circuits ortransmitting/receiving devices that can be described based on commonunderstanding of the technical field to which the present inventionpertains can be used.

Meanwhile, as with uplink signals, radio frequency signals that arereceived in each transmitting/receiving antenna 101 are amplified ineach amplifying section 102. Each transmitting/receiving section 103receives uplink signals amplified in the amplifying sections 102. Thereceived signals are converted into the baseband signal throughfrequency conversion in the transmitting/receiving sections 103 andoutput to the baseband signal processing section 104.

In the baseband signal processing section 104, the user data that isincluded in the input uplink signals is subjected to a fast Fouriertransform (FFT) process, an inverse discrete Fourier transform (IDFT)process, error correction decoding, a MAC retransmission controlreceiving process and RLC layer and PDCP layer receiving processes, andthe result is forwarded to the higher station apparatus 30 via thecommunication path interface 106. The call processing section 105performs call processing such as setting up and releasing communicationchannels, manages the state of the radio base station 10 and manages theradio resources.

The communication path interface 106 transmits and receives signals toand from the higher station apparatus 30 via a predetermined interface.The communication path interface 106 transmits and receives signals toand from neighboring radio base stations 10 (backhaul signaling) via aninter-base station interface (for example, optical fiber, the X2interface, etc.). For example, the communication path interface 106 maytransmit and receive TDD UL/DL configurations, special subframeconfigurations, sensing subframe configurations, sensing patterns and soon with neighboring radio base stations 10.

FIG. 17 is a diagram to show an example of a functional structure of aradio base station according to the present embodiment. Note that,although FIG. 17 primarily shows functional blocks that pertain tocharacteristic parts of the present embodiment, the radio base station10 has other functional blocks that are necessary for radiocommunication as well.

As shown in FIG. 17, the baseband signal processing section 104 providedin the radio base station 10 has a control section (scheduler) 301, atransmission signal generating section 302, a mapping section 303 and areceiving process section 304.

The control section (scheduler) 301 controls the scheduling of (forexample, allocates resources to) downlink data signals that aretransmitted in the PDSCH and downlink control signals that arecommunicated in the PDCCH and/or the enhanced PDCCH (EPDCCH). Also, thecontrol section 301 controls the scheduling of downlink referencesignals such as system information, synchronization signals, the CRS(Cell-specific Reference Signal), the CSI-RS (Channel State InformationReference Signal) and so on. Also, the control section 301 also controlsthe scheduling of uplink data signals that are transmitted in the PUSCH,uplink control signals that are transmitted in the PUCCH and/or thePUSCH, RA preambles that are transmitted in the PRACH, and so on. Notethat, when a licensed band and an unlicensed band are scheduled with onecontrol section (scheduler) 301, the control section 301 might controlcommunication in licensed band cells and unlicensed band cells. For thecontrol section 301, a controller, a control circuit or a control devicethat can be described based on common understanding of the technicalfield to which the present invention pertains can be used.

Also, the control section 301 controls the sensing patterns and/or thesensing subframe configurations which the user terminals 20 use. Forexample, the control section 301 may determine sensing patterns inassociation with TDD UL/DL configurations (first embodiment). Also, thecontrol section 301 may determine sensing patterns without associatingthese with TDD UL/DL configurations (second embodiment).

Note that the control section 301 may judge the state of interference inthe radio base station 10 and/or the user terminals 20 by using themeasurement results in the receiving process section 304, feedbackreports from the user terminals 20, and so on, and determine the sensingpatterns and/or the sensing subframe configurations. Also, the number ofuser terminals in cells, each user terminal's priority in transmission,uplink/downlink traffic and so on may be used to determine the sensingpatterns and/or the sensing subframe configurations.

The control section 301 outputs the determined sensing patterns and/orsensing subframe configurations to the transmission signal generatingsection 302, and controls the mapping section 303 to map signalsincluding these pieces of information. Note that the sensing patternsand/or the like may be associated with other pieces of information andreported implicitly, instead of being reported in explicit signals.

The transmission signal generating section 302 generates DL signals(downlink control signals, downlink data signals, downlink referencesignals and so on) based on commands from the control section 301, andoutputs these signals to the mapping section 303. For example, thetransmission signal generating section 302 generates DL assignments,which report downlink signal allocation information, and UL grants,which report uplink signal allocation information, based on commandsfrom the control section 301. Also, the downlink data signals aresubjected to a coding process and a modulation process, based on codingrates and modulation schemes that are determined based on channel stateinformation (CSI) from each user terminal 20. For the transmissionsignal generating section 302, a signal generator or a signal generatingcircuit that can be described based on common understanding of thetechnical field to which the present invention pertains can be used.

The mapping section 303 controls the allocation of the downlink signalsgenerated in the transmission signal generating section 302 to radioresources based on commands from the control section 301. For themapping section 303, a mapping circuit or a mapper that can be describedbased on common understanding of the technical field to which thepresent invention pertains can be used.

The receiving process section 304 performs receiving processes (forexample, demapping, demodulation, decoding and so on) of UL signals (forexample, delivery acknowledgement signals (HARQ-ACK), data signals thatare transmitted in the PUSCH and so on) transmitted from the userterminals. Also, the receiving process section 304 may measure thereceived power (RSRP), channel states and so on by using the receivedsignals. Note that the processing results and measurement results may beoutput to the control section 301. For the receiving process section304, a signal processor/measurer, or a signal processingcircuit/measurement circuit that can be described based on commonunderstanding of the technical field to which the present inventionpertains can be used.

Also, the receiving process section 304 receives and demodulates thePUSCH in the radio resources designated by predetermined information,based on commands from the control section 301.

FIG. 18 is a diagram to show an example of an overall structure of auser terminal according to the present embodiment. A user terminal 20has a plurality of transmitting/receiving antennas 201 for MIMOcommunication, amplifying sections 202, transmitting/receiving sections203, a baseband signal processing section 204 and an application section205. Note that the transmitting/receiving sections 203 may be comprisedof transmitting sections and receiving sections.

Radio frequency signals that are received in a plurality oftransmitting/receiving antennas 201 are each amplified in the amplifyingsections 202. Each transmitting/receiving section 203 receives thedownlink signals amplified in the amplifying sections 202. The receivedsignals are subjected to frequency conversion and converted into thebaseband signal in the transmitting/receiving sections 203, and thenoutput to the baseband signal processing section 204. For thetransmitting/receiving sections 203, transmitters/receivers,transmitting/receiving circuits or transmitting/receiving devices thatcan be described based on common understanding of the technical field towhich the present invention pertains can be used. Thetransmitting/receiving sections 203 are capable oftransmitting/receiving UL/DL signals in unlicensed bands. Note that thetransmitting/receiving section 203 may be capable oftransmitting/receiving UL/DL signals in licensed bands as well.

In the baseband signal processing section 204, the baseband signals thatare input are subjected to an FFT process, error correction decoding, aretransmission control receiving process and so on. Downlink user datais forwarded to the application section 205. The application section 205performs processes related to higher layers above the physical layer andthe MAC layer, and so on. Furthermore, in the downlink data, broadcastinformation is also forwarded to the application section 205.

Meanwhile, uplink user data is input from the application section 205 tothe baseband signal processing section 204. In the baseband signalprocessing section 204, a retransmission control transmission process(for example, an HARQ transmission process), channel coding, precoding,a discrete Fourier transform (DFT) process, an IFFT process and so onare performed, and the result is forwarded to eachtransmitting/receiving section 203. The baseband signal that is outputfrom the baseband signal processing section 204 is converted into aradio frequency band in the transmitting/receiving sections 203. Theradio frequency signals that are subjected to frequency conversion inthe transmitting/receiving sections 203 are amplified in the amplifyingsections 202, and transmitted from the transmitting/receiving antennas201.

FIG. 19 is a diagram to show an example of a functional structure of auser terminal according to the present embodiment. Note that, althoughFIG. 19 primarily shows functional blocks that pertain to characteristicparts of the present embodiment, the user terminal 20 has otherfunctional blocks that are necessary for radio communication as well.

As shown in FIG. 19, the baseband signal processing section 204 providedin the user terminal 20 has a control section 401, a transmission signalgenerating section 402, a mapping section 403 and a receiving processsection 404.

The control section 401 acquires the downlink control signals (signalstransmitted in the PDCCH/EPDCCH) and downlink data signals (signalstransmitted in the PDSCH) transmitted from the radio base station 10from the received signal processing section 404. The control section 401controls the generation of uplink control signals (for example, deliveryacknowledgement signals (HARQ-ACK) and so on) and uplink data signalsbased on the results of judging whether or not retransmission control isnecessary for downlink control signals, downlink data signals and so on.To be more specific, the control section 401 controls the transmissionsignal generating section 402 and the mapping section 403. For thecontrol section 401, a controller or a control device that can bedescribed based on common understanding of the technical field to whichthe present invention pertains can be used.

Also, the control section 401 has a function for learning the buffersize of UL data that is input from the application section 205, and,when there is UL data, controls the receiving process section 404 tocarry out UL-LBT in sensing subframes. Note that it is equally possibleto make the receiving process section 404 perform UL-LBT even when thereis no UL data.

Also, the control section 401 may apply control so that information thatis useful for PUSCH transmission is transmitted in the report period inaccordance with the results of LBT input from the receiving processsection 404.

The control section 401 controls predetermined subframes as sensingsubframes based on the sensing pattern. For example, the control section401 may learn the sensing pattern from an explicit report (first andsecond embodiments), or learn the sensing pattern implicitly (secondembodiment). For example, the control section 401 may count the numberof times sensing is tried in the receiving process section 404, andcalculate and acquire the sensing pattern based on the number of timessensing is tried (see, for example, table 1).

Also, the control section 401 may switch between using each sensingsubframe as a sensing subframe and as a special subframe (thirdembodiment). For example, when a subframe is designated as a sensingsubframe, the control section 401 controls the receiving process section404 to try receiving the PDCCH in a predetermined OFDM symbol periodbased on the PCFICH. Then, when a report arrives from the receivingprocess section 404 to the effect that a DL assignment has been detectedin the sensing subframe, the control section 401 makes the receivingprocess section 404 carry out DL reception or carry out UL-LBT.

The transmission signal generating section 402 generates UL signals(uplink control signals, uplink data signals, uplink reference signalsand so on) based on commands from the control section 401, and outputsthese signals to the mapping section 403. For example, the transmissionsignal generating section 402 generates uplink control signals such asdelivery acknowledgement signals (HARQ-ACK), channel state information(CSI) and so on, based on commands from the control section 401. Also,the transmission signal generating section 402 generates uplink datasignals based on commands from the control section 401. Note that, whena UL grant is contained in a downlink control signal reported from theradio base station, the control section 401 commands the uplink datasignal 403 to generate an uplink data signal. For the transmissionsignal generating section 402, a signal generator or a signal generatingcircuit that can be described based on common understanding of thetechnical field to which the present invention pertains can be used.

The mapping section 403 maps the uplink signals generated in thetransmission signal generating section 402 to radio resources based oncommands from the control section 401, and outputs these to thetransmitting/receiving sections 203. For the mapping section 403, amapping circuit or a mapper that can be described based on commonunderstanding of the technical field to which the present inventionpertains can be used.

The receiving process section 404 performs receiving processes (forexample, demapping, demodulation, decoding and so on) of the DL signalstransmitted in licensed bands and unlicensed bands (for example,downlink control signals transmitted from the radio base station,downlink data signals transmitted in the PDSCH, and so on). Whenreceiving the TDD UL/DL configuration, the special subframeconfiguration, the sensing subframe configuration, the sensing patternand so on from the radio base station 10, the receiving process section404 outputs these to the control section 401. Also, the receivingprocess section 404 may measure the received power (RSRP), channelstates and so on by using these received signals. Note that theprocessing results and measurement results may be output to the controlsection 401. For the receiving process section 404, a signalprocessor/measurer, or a signal processing circuit/measurement circuitthat can be described based on common understanding of the technicalfield to which the present invention pertains can be used.

The receiving process section 404 executes LBT in an unlicensed band byusing predetermined subframes (for example, special subframes) assensing subframes based on commands from the control section 401, andoutputs the results of LBT (for example, the results of judging whetheror not the channel state is clear or busy) to the control section 401.

Also, in a subframes that are designated as a sensing subframe, thereceiving process section 404 tries to receive the PDCCH in apredetermined OFDM symbol period based on commands from the controlsection 401, based on the PCFICH. Then, when the receiving processsection 404 detects a DL assignment to designate the PDSCH for thesubject terminal, the receiving section 404 sends a report to thateffect to the control section 401.

Note that the block diagrams that have been used to describe the aboveembodiments show blocks in function units. These functional blocks(components) may be implemented in arbitrary combinations of hardwareand software. Also, means for implementing each functional block is notparticularly limited. That is, each functional block may be implementedwith one physically-integrated device, or may be implemented byconnecting two physically separate devices via radio or wire and usingthese multiple devices.

For example, part or all of the functions of radio base stations 10 anduser terminals 20 may be implemented using hardware such as ASICs(Application-Specific Integrated Circuits), PLDs (Programmable LogicDevices), FPGAs (Field Programmable Gate Arrays), and so on. Also, theradio base stations 10 and the user terminals 20 may be implemented witha computer device that includes a processor (CPU), a communicationinterface for connecting with networks, a memory and a computer-readablestorage medium that holds programs.

Here, the processor and the memory are connected with a bus forcommunicating information. Also, the computer-readable recording mediumis a storage medium such as, for example, a flexible disk, anoptomagnetic disk, a ROM, an EPROM, a CD-ROM, a RAM, a hard disk and soon. Also, the programs may be transmitted from the network through, forexample, electric communication channels. Also, the radio base stations10 and the user terminals 20 may include input devices such as inputkeys and output devices such as displays.

The functional structures of the radio base stations 10 and the userterminals 20 may be implemented with the above-described hardware, maybe implemented with software modules that are executed on the processor,or may be implemented with combinations of both. The processor controlsthe whole of the user terminals by allowing the operating system towork. Also, the processor reads programs, software modulates and datafrom the storage medium into the memory, and executes various types ofprocesses. Here, these programs have only to be programs that make acomputer execute each operation that has been described with the aboveembodiments. For example, the control section 401 of the user terminals20 may be stored in the memory and implemented by a control program thatoperates on the processor, and other functional blocks may beimplemented likewise.

Now, although the present invention has been described in detail above,it should be obvious to a person skilled in the art that the presentinvention is by no means limited to the embodiments described herein.For example, the above-described embodiments may be used individually orin combinations. The present invention can be implemented with variouscorrections and in various modifications, without departing from thespirit and scope of the present invention defined by the recitations ofclaims. Consequently, the description herein is provided only for thepurpose of explaining examples, and should by no means be construed tolimit the present invention in any way.

The disclosure of Japanese Patent Application No. 2014-156209, filed onJul. 31, 2014, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

1. A user terminal that can communicate with a radio base station byusing an unlicensed band, the user terminal comprising: a receivingprocess section that detects a channel state in the unlicensed band byperforming LBT (Listen Before Talk) in a sensing subframe; and a controlsection that controls a predetermined subframe as the sensing subframebased on a sensing pattern.
 2. The user terminal according to claim 1,wherein the sensing pattern is associated with a TDD UL/DLconfiguration.
 3. The user terminal according to claim 2, wherein thepredetermined subframe is a special subframe in the TDD UL/DLconfiguration.
 4. The user terminal according to claim 2, wherein thesensing subframe comprises an LBT period to perform LBT, a guard periodfor switching between transmission and reception, and a report period totransmit predetermined information about PUSCH transmission.
 5. The userterminal according to claim 4, wherein the lengths of the LBT period,the guard period and the report period are equivalent to the lengths ofa DwPTS (Downlink Pilot Time Slot), a GP (Guard Period), and a UpPTS(Uplink Pilot Time Slot) in a special subframe in the TDD UL/DLconfiguration, respectively.
 6. The user terminal according to claim 1,wherein the control section calculates and acquires the sensing patternbased on a predetermined rule.
 7. The user terminal according to claim3, wherein, when a DL assignment is detected in the predeterminedsubframe, the control section controls the subframe as a specialsubframe.
 8. A radio base station that communicates with a user terminalthat can use an unlicensed band, the radio base station comprising: acontrol section that controls a sensing pattern which the user terminaluses; and a transmission section that transmits the sensing pattern tothe user terminal, wherein the sensing pattern is information about atiming in which the user terminal performs LBT (Listen Before Talk) inthe unlicensed band.
 9. A radio communication method for a user terminalthat can communicate with a radio base station by using an unlicensedband, the radio communication method comprising the steps of: detectinga channel state in the unlicensed band by performing LBT (Listen BeforeTalk) in a sensing subframe; and controlling a predetermined subframe asthe sensing subframe based on a sensing pattern.
 10. A radiocommunication system comprising a user terminal and a radio base stationthat can communicate by using an unlicensed band, wherein the userterminal comprises: a receiving process section that detects a channelstate in the unlicensed band by performing LBT (Listen Before Talk) in asensing subframe; and a control section that controls a predeterminedsubframe as the sensing subframe based on a sensing pattern.
 11. Theuser terminal according to claim 3, wherein the sensing subframecomprises an LBT period to perform LBT, a guard period for switchingbetween transmission and reception, and a report period to transmitpredetermined information about PUSCH transmission.